Receiver and its tracking adjusting method

ABSTRACT

A receiver such that the period required for tracking adjustment, temperature compensation is not needed, and tracking errors due to fluctuation of the power supply voltage are prevented from increasing, and a tracking adjusting method for the receiver. A DAC  4  generates a voltage according to the value of data (Do) inputted from an MPU  81  by using a control voltage outputted from a low-pass filter  35  in a local oscillator  3  as a reference voltage used during digital-analog conversion. A multiplier circuit  5  analog-multiplies the output voltage of the DAC  4  by a predetermined multiplier. The output voltage of the multiplier circuit  5  is applied as a tuning voltage to a high-frequency tuning circuit  20 . In an EEPROM  84  stored is the value of the input data (Do) of the DAC  4  which has been measured in advance and corresponds to the tuned voltage of when the tracking error is the minimum at the central value of the local oscillation frequency, and the MPU  81  reads the data (Do) from the EEPROM  84  and inputs it to the DAC  4.

TECHNICAL FIELD

The present invention relates to a receiver which adopts asuperheterodyne system, and its tracking adjusting method.

BACKGROUND ART

Generally, in receivers which receive broadcast waves such as AMbroadcast and FM broadcast, a superheterodyne system is adopted as areceiving system. The superheterodyne system is a receiving system whichconverts a received broadcast signal into an intermediate frequencysignal, which has a fixed frequency independent of an frequency of areceived signal (receive frequency), by mixing a predetermined localoscillation signal to the received broadcast signal, and reproduces asound signal by performing detection processing, amplification, etc.after that, and has a feature that it is superior to other receivingsystems in sensitivity, selectivity, etc.

FIG. 8 is a diagram showing the structure of a conventional receiverwhich adopts the superheterodyne system. The conventional receiver shownin this diagram is constituted by including an antenna 200, a highfrequency receiving circuit 202, a local oscillator 204, a mixingcircuit 206, an intermediate frequency amplifier circuit 208, an MPU210, memory 212, a control unit 214, and a digital-to-analog converter(DAC) 216.

In the conventional receiver, data showing the relation between a tunedvoltage applied to the high frequency receiving circuit 202 and areceived frequency is stored in the memory 212. The MPU 210 calculatesdata necessary for generating a tuned voltage on the basis of the datastored in the memory 212 to input it into the DAC 216. The tuned voltagewhich has a desired value is generated by this DAC 216, and is appliedto the high-frequency tuning circuit 202.

FIG. 9 is a graph showing the contents of the data stored in the memory212. As shown in this graph, let a variable range of the receivedfrequency be f₀ to f₅, and in this variable range, for example, tunedvoltages V₀, V₁, V₂, V₃, V₄, and V₅ corresponding to some receivedfrequencies f₀, f₁, f₂, f₃, f₄, and f₅ are measured beforehand, andinput data to the DAC 216 necessary for generating these plural tunedvoltages is stored in the memory 212. Then, in the case of setting thereceived frequency of the high frequency receiving circuit 202 as avalue other than f₀, f₁, f₂, f₃, f₄, and f₅ which are mentioned above,the MPU 210 obtains input data necessary for generating a desiredreceived frequency by reading the input data of the DAC 216corresponding to two received frequencies in the vicinity of it from thememory 212 and performing linear interpolating operation to input thisinto the DAC 216. Thus, a predetermined tuned voltage is applied to thehigh frequency receiving circuit 202 from the DAC 216, and the desiredreceived frequency is set.

By the way, in the case of setting a tuning frequency of the highfrequency receiving circuit 202 with interlocking with an oscillationfrequency of the local oscillator 204 by using the conventional systemmentioned above, there have been problems: (1) a tracking adjustmenttakes time, (2) temperature compensation is difficult, and (3) it isweak to the fluctuation of a supply voltage.

As mentioned above, in order to set a suitable tuned voltage by usingthe DAC 216, it is necessary to perform the tracking adjustment ofmeasuring beforehand a plurality of tuned voltages V₀, V₁, V₂, V₃, V₄,and V₅ as shown in FIG. 9. For example, to measure a tuned voltage V₀ isto obtain the tuned voltage V₀ at which a tracking error becomes at aminimum, by changing a value of input data of the DAC 216 in the stateof outputting a local oscillation signal at a frequency corresponding tothe tuning frequency f₀ from the local oscillator 204. Usually, it ismeasured by using a distortion meter and a level meter whether atracking error is at a minimum, and the distortion rate measurementusing the distortion meter takes time of about 10 to 20 seconds forwaiting for the stability of an output value. Since such measurement isrequired every tuned voltage, it takes much time for the trackingadjustment.

In addition, generally in the high frequency receiving circuit 202,since characteristics of devices used change with temperature, a tuningfrequency changes with temperature even if a tuned voltage outputtedfrom the DAC 216 is constant. On the other hand, since the localoscillator 204 generally has the phase synchronous loop (PLL) structureof including a voltage controlled oscillator and a variable frequencydivider, the frequency of a local oscillation signal determined by adivision ratio of the variable frequency divider does not change even ifcharacteristics of devices used change with temperature. Thus, sinceonly the tuning frequency changes with interlocking with a temperaturechange but the frequency of the local oscillation signal does notchange, a tracking error increases in connection with the temperaturechange. Although it is necessary to equip with a temperaturecompensation circuit newly in order to avoid such inconvenience, it isnot easy to prevent the increase of the tracking error by performingtemperature compensation over the entire range of the tuning frequency,and further, there newly arises a problem that a circuit scale becomelarge.

Furthermore, when a supply voltage of the receiver shown in FIG. 8fluctuates, for example, when a drive voltage drops in a pocket receiverdriven by a battery, a car radio driven by an vehicle-mounted battery,or the like, an output voltage of the DAC 216 becomes low withinterlocking with the drop of the supply voltage, and hence, a trackingerror becomes large since a tuned voltage drops even if the MPU 210intends to set a desired tuning frequency.

DISCLOSURE OF THE INVENTION

The present invention is created in view of such points, and aims atproviding a receiver and its tracking adjusting method which can shortenthe time required for tracking adjustment, does not require temperaturecompensation, and can prevent a tracking error from increasing becauseof the fluctuation of a supply voltage.

In order to solve the issues mentioned above, the receiver of thepresent invention comprises a high frequency receiving circuit, a localoscillator, a mixing circuit, an offset circuit, and a multipliercircuit. The high frequency receiving circuit receives a broadcast waveat a received frequency according to a tuned voltage. The localoscillator generates a local oscillation signal at a frequency accordingto a control voltage. The mixing circuit mixes the signal, which isoutputted from the high frequency receiving circuit, and localoscillation signal, and outputs an intermediate frequency signalcorresponding to a differential frequency thereof. The offset circuitsets a predetermined offset voltage to a control voltage. The multipliercircuit performs the analog multiplication of a predetermined multiplierto the control voltage. By such structure, the receiving circuit of thepresent invention applies a voltage, which is the control voltage passedthrough the offset circuit and multiplier circuit, as a tuned voltage tothe high frequency receiving circuit.

Since the tuned voltage is generated on the basis of the controlvoltage, it is not necessary to obtain a plurality of tuned voltages, atwhich a tracking error becomes at a minimum, by measurement like aconventional receiver using a digital-to-analog converter, and hence, itis possible to shorten the time necessary for tracking adjustment.

In addition, it is desirable to set the above-mentioned multiplier ofthe multiplier circuit on the basis of a variable range of a frequencyof a local oscillation signal generated by the local oscillator and avariable range of a received frequency of the high frequency receivingcircuit. Since a center frequency of the variable range of the localoscillation signal and a center frequency of the variable range of thereceived frequency of the high frequency receiving circuit shifts by theintermediate frequency, even if respective variable widths are madeequal, the variable width of the control voltage and the variable widthof the tuned voltage which correspond to these variable ranges do notbecome equal, but, by analog-multiplying the control voltage by thepredetermined multiplier, it becomes possible to make the differencebetween the variable widths of these respective voltages coincide.

In addition, it is desirable to set an offset voltage by achieving theabove-mentioned offset circuit by the digital-to-analog converter usingthe control voltage as a reference voltage, and adjusting input data.Since it is possible to make a value of the offset voltage variable byadjusting a value of digital input data, it becomes possible to adjustthe offset voltage by using a processor etc., and hence, it is possibleto reduce the effort and time which is necessary for the setting of theoffset voltage. In addition, since the value of the tuned voltageapplied to the high frequency receiving circuit is also interlocked andis fluctuated with the control voltage when ambient temperature changesand the value of the control voltage is fluctuated, it becomes possibleto perform temperature compensation only by making the high frequencyreceiving circuit and local oscillator in similar structure, and hence,temperature compensation by a complicated circuit becomes unnecessary.

In addition, it is desirable to set the above-mentioned offset voltageso that a tracking error may become at a minimum when setting afrequency of the local oscillation signal at an arbitrary value includedin its variable range. It is possible to shorten the time necessary fortracking adjustment by reducing the number of times of this adjustmentby using a distortion meter etc.

Furthermore, it is desirable to prepare a plurality of values which ischangeable according to a frequency of the local oscillation signal, andto set the offset voltage so that a tracking error corresponding to theentire area of the variable range of the frequency of the localoscillation signal may become a predetermined value or less. Althoughoptimal tracking adjustment in the central value of the variablefrequency range of the local oscillation signal is performed and apredetermined offset voltage corresponding to the frequency range inthis vicinity is set, there is a tendency that a tracking error becomeslarge as the frequency of the local oscillation signal shifts from thiscentral value. For this reason, it is possible to easily lessen atracking error in the entire area of the variable frequency range bydividing the entire area of the variable frequency range of the localoscillation signal into a plurality of areas, setting the offset voltagewhich has a different value every divided area, and switching the offsetvoltage every divided area.

Moreover, it is desirable to comprise memory, which stores input datanecessary for the generation of the offset voltage set so that atracking error corresponding to the entire area of the variable range ofthe frequency of the local oscillation signal mentioned above may becomea predetermined value or less, and a voltage value setting unit whichsets a value of the offset voltage corresponding to the frequency of thelocal oscillation signal by reading input data, stored in this memory,and inputting it into the digital-to-analog converter. Since it ispossible to generate an optimal offset voltage by reading input datastored in the memory and inputting it into the digital-to-analogconverter, it becomes easy to set an offset voltage after the optimaladjustment is performed.

In addition, in a tracking adjusting method of the receiver of thepresent invention, while setting a received frequency of the receiver atan arbitrary value included in its variable range at a first step, apredetermined test signal having the same frequency as the receivedfrequency at this time is inputted into the high frequency receivingcircuit. At a second step, a value of the offset voltage set by theoffset circuit is set so that a tracking error of the receiver aftervarious kinds of settings being performed at the first step may becomeat a minimum. Since measurement of a tracking error is executed in anarbitrary value included in the variable range of a received frequency,it is possible to shorten the time necessary for the tracking adjustmentby reducing the number of times of this measurement.

Furthermore, it is desirable to have a third step of changing andsetting a value of the offset voltage in regard to some frequency bandin which these upper limit or lower limit is included when a trackingerror near the upper limit or lower limit of the variable range of thereceived frequency is large after the above-mentioned second step.Although there is also the case that a tracking error in the entirereceived band does not become a predetermined value or less only by thetracking adjustment at one point of an arbitrary value, it is possibleto easily suppress the tracking error in the entire received band withina predetermined tolerance by changing a value of the offset voltagecorresponding to some frequency band containing the upper limit or lowerlimit of the received frequency where the tracking error becomes large.

Moreover, in a tracking adjusting method of the receiver of the presentinvention, while setting a received frequency of the receiver at anarbitrary value included in its variable range at a fourth step, apredetermined test signal having the same frequency as the receivedfrequency at this time is inputted into the receiver. At a fifth step,input data of the digital-to-analog converter is set so that a trackingerror of the receiver after various kinds of settings being performed atthe fourth step may become at a minimum. In the sixth step, the inputdata set in the fifth step is stored in the memory. Since themeasurement of a tracking error is executed in an arbitrary valueincluded in the variable range of a received frequency, it is possibleto shorten the time necessary for the tracking adjustment by reducingthe number of times of this measurement. In addition, since the resultof tracking adjustment is stored in the memory, the storage andsubsequent utilization of this resultant data become easy.

Furthermore, it is desirable to have after the above-mentioned sixthstep a seventh step of changing and setting contents of input data ofthe digital-to-analog converter in regard to some frequency band inwhich the upper limit or lower limit is included when a tracking errornear these upper limit or lower limit of the variable range is large,and an eighth step of storing in the memory the input data of thedigital-to-analog converter after the change set at this seventh step.Although it is necessary to set a plurality of offset voltages which hasdifferent values if it is not possible to suppress the tracking error toa predetermined permissible value or less only by setting the offsetvoltage which has a common value in the entire receiving band, thestorage and utilization of resultant data of the tracking adjustmentbecome easy since what is necessary is just to store the data,corresponding to the values of the plurality of offset voltages, in thememory even if it is such a case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the structure of an FM receiver of anembodiment;

FIG. 2 is a graph showing the relationship between the output values ofa distortion meter and a level meter, and the tuning point;

FIG. 3 is a flowchart showing the operation procedure of trackingadjustment performed by PC control;

FIG. 4 is a flowchart showing the operation procedure of trackingadjustment performed by PC control;

FIG. 5 is a graph showing the relationship between the local oscillationfrequency and the tuning frequency;

FIG. 6 is a graph showing the relationship between the variable range ofa local oscillation frequency, and the tracking error;

FIG. 7 is a graph showing the relationship between the variable range ofa local oscillation frequency, and the tracking error;

FIG. 8 is a diagram showing the structure of a conventional receiverwhich adopts a superheterodyne system; and

FIG. 9 is a graph showing contents of data stored in memory.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, an FM receiver according to an embodiment where the presentinvention is applied will be described with referring to drawings.

FIG. 1 is a diagram showing the structure of an FM receiver of thisembodiment. An FM receiver 100 shown in this diagram is constituted byincluding an antenna 1, an high frequency receiving circuit 2, a localoscillator 3, two digital-to-analog converter (DAC) 4 and 6, twomultiplier circuits 5 and 7, a control section 8, a mixing circuit 9, anintermediate frequency amplifier circuit 10, a detection circuit 11, alow frequency amplifier 12, and a speaker 13.

The high frequency receiving circuit 2 performs high frequencyamplification of a signal after tuning while performing the tuningoperation of selectively passing only a component near a predeterminedtuning frequency to a broadcast wave inputted from the antenna 1, and isconstituted by including two high-frequency tuning circuits 20 and 24,and a high frequency amplifier 22.

Selectivity is increased by magnifying an output of a first stage ofhigh-frequency tuning circuit 20, to which the antenna 1 is connected,by the high frequency amplifier 22, and further passing the amplifiedoutput to the second stage of high-frequency tuning circuit 24. Inaddition, since a variable capacitance diode for changing a tuningfrequency is included in each of the two high-frequency tuning circuits20 and 24, the tuning frequency of each of the high-frequency tuningcircuits 20 and 24 is changed with interlocking, by changing a reversebias of tuned voltage applied to the variable capacitance diode. Thatis, in the high frequency receiving circuit 2, a broadcast wave at areceived frequency (tuning frequency) according to the tuned voltageapplied to two high-frequency tuning circuits 20 and 24 is selected.

The local oscillator 3 is constituted by including a voltage controlledoscillator (VCO) 31, a frequency divider 32, a reference signalgenerator 33, a phase comparator 34, and a low-pass filter (LPF) 35.

The VCO 31 performs the oscillation operation of a frequencycorresponding to the control voltage generated by the low-pass filter 35to output a local oscillation signal, and comprises a VCO resonancecircuit 91 and an amplifier 92. The VCO resonance circuit 91 is aparallel resonance circuit which consists of an inductor and acapacitor, and two variable capacitance diodes for making a resonancefrequency variable are connected in parallel to the capacitor. Then,when the capacity of the variable capacitance diodes changes accordingto the reverse bias of control voltage applied, the resonance frequencyof the VCO resonance circuit 91 changes. In addition, the amplifier 92performs a predetermined magnifying operation necessary for oscillation.

The frequency divider 32 performs the frequency division of the localoscillation signal inputted from the VCO 31 by a predetermined divisionratio N and outputs it. A value N of the division ratio is set as beingvariable by the control section 8. The reference signal generator 33outputs a reference signal at a predetermined frequency with highfrequency-stability.

The phase comparator 34 performs phase comparison between the referencesignal outputted from the reference signal generator 33, and the signal(local oscillation signal after division) outputted from the frequencydivider 32, and outputs a pulse-like error signal according to the phasedifference. The low-pass filter 35 generates the control voltage byperforming smoothing by removing a high frequency component of thepulse-like error signal outputted from the phase comparator 34. TheseVCO 31, frequency divider 32, phase comparator 34, and low-pass filter35 are connected in a loop to constitute a phase synchronous loop (PLL).

In addition, the respective variable capacitance diodes included in thehigh-frequency tuning circuits 20 and 24 in the high frequency receivingcircuit 2 mentioned above and the variable capacitance diode included inthe VCO resonance circuit 91 in the local oscillator 3, which are used,have the almost same voltage vs. capacity characteristics.

The DAC 4 and multiplier circuit 5 are used for generating a tunedvoltage applied to the high-frequency tuning circuit 20 in the highfrequency receiving circuit 2. Specifically, the DAC 4 of thisembodiment generates a voltage according to a value of the digital datainputted from the control section 8 by using a control voltage Vcoutputted from the low-pass filter 35 in the local oscillator 3 as areference voltage at the time of digital-to-analog conversion. Inaddition, it is made in the following explanation that the digital datainputted from the control section 8 to the DACs 4 and 6 respectively iscalled “DAC input data”.

When n-bit DAC input data D is inputted by the control section 8, theoutput voltage Va of the DAC 4 is expressed like the following formula.Va=Vc×(D/2^(n))  (1)

In formula (1), supposing that the value of DAC input data D inputtedinto the DAC 4 is fixed to a predetermined value, the output voltage Vaof the DAC 4 changes according to the control voltage Vc outputted fromthe low-pass filter 35. In addition, a method of setting the value ofthe DAC input data inputted into the DAC 4 will be described later.

The multiplier circuit 5 analog-multiplies the output voltage Va of theDAC 4 by a predetermined multiplier K. Specifically, the output voltageVr of the multiplier circuit 5 is expressed like the following formula.Vr=Va×K  (2)

It is made that some candidate values such as “1”, “1.5”, and “2” areprepared as the multiplier K of this multiplier circuit 5, and hence,anyone of the values can be set arbitrarily. Then, the value of themultiplier K is set on the basis of a variable range of a frequency ofthe local oscillation signal, and a variable range of a receivedfrequency in the high frequency receiving circuit 2. In this embodiment,since the frequency of the local oscillation signal outputted from thelocal oscillator 3 is set as a value higher by 10.7 MHz than a receivedfrequency in the high frequency receiving circuit 2, it is necessary toset the variable range of the tuned voltage applied to the highfrequency receiving circuit 2 wider than the variable range of thecontrol voltage generated in the local oscillator 3 if it is intended tomake the variable range of the received frequency and the variable rangeof the frequency of the local oscillation signal coincide, and hence,the multiplier circuits 5 and 7 are used. The output voltage Vr of themultiplier circuit 5 is applied to the high-frequency tuning circuit 20as a tuned voltage Vt1.

In addition, the DAC 6 and multiplier circuit 7 are used for generatinga tuned voltage applied to the high-frequency tuning circuit 24 in thehigh frequency receiving circuit 2. The DAC 6 outputs the output voltageVa according to the DAC input data inputted from the control section 8,and the control voltage Vc outputted from the low-pass filter 35 likethe DAC 4 mentioned above. The multiplier circuit 7 analog-multipliesthe output voltage Va of the DAC 6 by a predetermined multiplier K likethe multiplier circuit 5 mentioned above. The output voltage Vr of themultiplier circuit 7 is applied to the high-frequency tuning circuit 24as a tuned voltage Vt2.

The above-mentioned DACs 4 and 6 correspond to offset circuits, and thedifference between the output voltage and input voltage of each of theseDACs 4 and 6 corresponds to the offset voltage.

The control section 8 controls the entire operation of the FM receiver100, and is constituted by including an MPU 81, an interface section(I/F) 82, a control section 83, and EEPROM 84.

The MPU 81 performs predetermined control operation of setting thedivision ratio N of the frequency divider 32 in the local oscillator 3according to the setting value of the received frequency inputted fromthe operation section 83, and setting the DAC input data correspondingto each of the DACs 4 and 6.

The interface section 82 is for the connection between an externalpersonal computer (PC) 128 and the MPU 81 in the control section 8.Various commands can be given from the PC 128 to the MPU 81 through thisinterface section 82.

The operation section 83 is equipped with various kinds of operationkeys, and is used for the setting of the received frequency, and thelike. The EEPROM 84 is memory which can perform the storage and erase ofdata electrically, and stores the DAC input data necessary forgenerating a predetermined offset voltage.

The mixing circuit 9 mixes a received signal, which is outputted fromthe high frequency receiving circuit 2, and a local oscillation signaloutputted from the local oscillator 3, and outputs a signalcorresponding to a differential component thereof.

The intermediate frequency amplifier circuit 10 generates anintermediate frequency signal by passing only the frequency componentnear the predetermined intermediate frequency (10.7 MHz) whilemagnifying the signal outputted from the mixing circuit 9.

The detection circuit 11 performs the detection processing of theintermediate frequency signal outputted from the intermediate frequencyamplifier circuit 10, and demodulates a sound signal. The low frequencyamplifier 12 amplifies the sound signal outputted from the detectioncircuit 11 at a predetermined gain. The speaker 13 performs a voiceoutput on the basis of the sound signal after the amplification which isoutputted from the low frequency amplifier 12.

A test signal input terminal 14 is provided for inputting a test signalat a predetermined frequency for performing tracking adjustment. Thetest signal inputted through this test signal input terminal 14 isinputted into the high frequency receiving circuit 2.

In addition, each of the distortion meter 120, level meter 122, testsignal generator 126, and PC 128 which are shown in FIG. 1 is used forperforming the predetermined tracking adjustment which sets a value ofthe DAC input data inputted into the DACs 4 and 6 in the FM receiver 100mentioned above.

The distortion meter 120 measures a distortion rate based on the soundsignal after the amplification which is outputted from the low frequencyamplifier 12 in the FM receiver 100. The level meter 122 measures asignal level of the sound signal after the amplification which isoutputted from the low frequency amplifier 12.

FIG. 2 is a graph showing the relationship between the output values ofthe distortion meter 120 and level meter 122, and the tuning point. Inthis diagram, the horizontal axis corresponds to the tuning frequency,the left-hand side vertical axis corresponds to the output value of thelevel meter 122, and the right-hand side vertical axis corresponds tothe output value of the distortion meter 120, respectively. In addition,a curve a shows the changing state of the output value of the distortionmeter 120, and a curve b shows the changing state of the output value ofthe level meter 122, respectively.

As shown in FIG. 2, at an optimum tuning point shown by a dotted linenear the center, the output value (distortion rate) of the distortionmeter 120 becomes at a minimum, and, the output value of the level meter122 becomes at a maximum. Hence, in order to investigate a tuned voltagecorresponding to the optimum tuning point, what is necessary is just todetect the tuned voltage that the output value of the level meter 122becomes at a maximum, but the changing degree near the tuning point ofthe output value of the level meter 122 is gentle, and hence, it is noteasy to extract the optimum tuning point. For this reason, usually, thetuned voltage that the output value of the distortion meter 120 becomesat a minimum is detected, which is set as the tuned voltagecorresponding to the optimum tuning point. However, since the outputvalue of the distortion meter 120 becomes at a minimum also in anon-signal status, it is also necessary to refer to the output value ofthe level meter 122 not to detect an incorrect tuning point in such astatus.

The test signal generator 126 outputs the test signal generated byapplying FM modulation to a carrier at a predetermined frequency on thebasis of a command from the PC 128. This test signal is inputted intothe high frequency amplifier 2 in the FM receiver 100 through the testsignal input terminal 14 mentioned above.

The PC 128 controls consecutive operation for performing the trackingadjustment. Specifically, the PC 128 sets the received frequency of theFM receiver 100 at the frequency of a test signal by setting thedivision ratio of the frequency divider 32 in the local oscillator 3 asa predetermined value while sending a command to the test signalgenerator 126 and inputting the predetermined test signal into the FMreceiver 100. In addition, in this status, the PC 128 reads each outputvalue of the distortion meter 120 and level meter 122 with changing avalue of the DAC input data inputted into the DACs 4 and 6 respectively,and measures the DAC input data at the time when the output value of thelevel meter 122 is a predetermined value or higher, and the output valueof the distortion meter 120 becomes at a minimum. The DAC input dataobtained for by this measurement is sent to the control section 8 of theFM receiver 100, and is stored in the EEPROM 84 by the MPU 81. The MPU81 mentioned above corresponds to the voltage value setting unit. Thedetailed procedure of the tracking adjustment will be described later.

The FM receiver 100 of this embodiment has such structure, and next, thedetail of the tracking adjustment operation performed by the PC 128 willbe explained.

FIGS. 3 and 4 are flowcharts showing the operation procedure of thetracking adjustment performed by the control of the PC 128. In addition,since the FM receiver 100 of this embodiment includes two DACs 4 and 6which become objects of the tracking adjustment, the case that thetracking adjustment is performed will be explained with paying attentionto any one of the DACs.

First, the PC 128 sends a command to the test signal generator 126 toinput the test signal at the same frequency as the center frequency ofthe variable range of the received frequency of the FM receiver 100 intothe FM receiver 100 (step 100). For example, supposing that the receivedfrequency band of the FM receiver 100 is 76.0 to 90.0 MHz, the testsignal at 83.0 MHz which is the same frequency as the center frequencyof this variable range is generated by the test signal generator 126,and is inputted into the test signal input terminal 14 of the FMreceiver 100.

In addition, the PC 128 sends a command to the control section 8 to setsuch that the oscillation frequency (local oscillation frequency) of thelocal oscillator 3 may become a frequency corresponding to the centerfrequency of the variable range of the received frequency of the FMreceiver 100 (step 101). For example, supposing that in the FM receiver100 of this embodiment a local oscillation signal with a frequencyhigher by 10.7 MHz than the received frequency is used, the divisionratio of the frequency divider 32 necessary for generating the localoscillation frequency of 93.7 MHz is set.

Thus, after the input of the test signal and the setting of the localoscillation frequency are finished, next, the PC 128 changes the valueof the DAC input data corresponding to one side of DAC 4 within thepredetermined range, and measures a value D₀ of the DAC input data atwhich the tracking error becomes at a minimum (step 102) to write thismeasurement value in the EEPROM 84 in the control section 8 (step 103).As mentioned above, since the output value of the distortion meter 120also becomes at a minimum when the tracking error becomes at a minimumby the optimum tuning point being set, the PC 128 changes the value ofthe DAC input data in one direction and measures the value of the DACinput data at which the output value of this distortion meter 120becomes at a minimum. In addition, at this time, the PC 128 verifiesthat the output value of the level meter 122 is the predetermined valueor higher, and if being less than the predetermined value, it performspredetermined error display.

FIG. 5 is a graph showing the relationship between the local oscillationfrequency and the tuning frequency. When there is no tracking error inthe entire area of the receiving band, the tuning frequency is set at afrequency lower by 10.7 MHz than this when the local oscillationfrequency is changed, and hence, the local oscillation frequency and thetuning frequency become the relationship shown by a straight line c inFIG. 5. However, generally, since a tracking error caused by respectivecircuit configuration of the local oscillator 3 and high frequencyreceiving circuit 2, the difference between the oscillation frequencyand tuning frequency, etc. arises, they have the relationship of a curved different from the straight line c mentioned above.

Since the DAC input data D₀ which makes the output value of thedistortion meter 120 at a minimum when a local oscillation frequency isset at the center frequency of a variable range is measured in themeasurement at step 102 mentioned above, it is possible to minimize thetracking error corresponding to this local oscillation frequency andtuning frequency by applying an output voltage to the high-frequencytuning circuit 20 as the tuned voltage Vt1 after passing the voltage,generated by the DAC 4 in correspondence to this DAC input data D₀, tothe multiplier circuit 5. That is, it is possible to fulfill therelationship between the local oscillation frequency and tuningfrequency as shown by a curve e in FIG. 5 by executing the measurementat step 102 and setting the value of the DAC input data corresponding tothe DAC 4.

Next, the PC 128 investigates whether a tracking error becomes apredetermined value or lower over the entire receiving band, and whenthe tracking error becomes large in some frequency band, it changes thevalue of the DAC input data in the frequency range in which this band isincluded.

Specifically, first, the PC 128 sends a command to the test signalgenerator 126 to input the test signal at the same frequency as theupper limit of the variable range of the received frequency of the FMreceiver 100 into the FM receiver 100 (step 104). In addition, the PC128 sends a command to the control section 8 to set a value of the localoscillation frequency so that it may become a frequency corresponding tothe upper limit fmax of the variable range of the local oscillationfrequency (step 105).

Thus, after various kinds of settings corresponding to the upper limitof the received frequency are finished, the PC 128 fetches the outputvalue of the level meter 122, and determines whether this value is thepredetermined value or higher (step 106). Thus, in this embodiment, itis determined in the upper limit of the received frequency byinvestigating the output value of the level meter 122 whether thetracking error is included in the tolerance of being a predeterminedvalue or less. Although the change of the output value of the levelmeter 122 becomes gentle near the optimum tuning point as shown in FIG.2, the output value of the level meter 122 greatly drops as beingseparates from the optimum tuning point, and hence, it is possible toeasily determine whether the tracking error becomes large with exceedingthe tolerance, only by referring to only the output value of this levelmeter 122.

When the tracking error becomes large and the output value of the levelmeter 122 drops to the predetermined value or lower, negative judgmentis performed in the determination at step 106, and next, the PC 128 setsa value obtained by subtracting or adding the predetermined value d₀from or to the DAC input data D₀ corresponding to a median fc mentionedbelow (step 107) as the DAC input data D₁ set when the local oscillationfrequency is higher than an upper mean value fu corresponding to thealmost middle between the median fc of the variable range, and the upperlimit fmax, and writes this setting value in the EEPROM 84 in thecontrol section 8 (step 108).

In addition, since such a value of do that the tracking error may becomea predetermined value or less in the upper limit fmax of the variablerange of the local oscillation frequency is calculated beforehand byinputting the DAC input data D₁, obtained by addition or subtraction ofthis predetermined value d₀, instead of the DAC input data D₀ into theDAC 4, it is made to be able to suppress the tracking error in the rangefrom the median fc to the upper limit value fmax to the predeterminedvalue or less only by changing the value of the DAC input data into D₁from D₀ at the frequency in a predetermined range including this upperlimit fmax when the tracking error in the upper limit fmax is large.

Furthermore, when the tracking error corresponding to the upper limitfmax of the local oscillation frequency is small and the output value ofthe level meter 122 is the predetermined value or higher, affirmativejudgment is performed in the determination at step 106, and next, the PC128 sets the value same as the DAC input data D₀ corresponding to themedian fc, mentioned above, as the DAC input data D₁ set when the localoscillation frequency is higher than the upper mean value f_(u)corresponding to the almost middle between the median fc of its variablerange and the upper limit fmax (step 109) to write this setting value inthe EEPROM 84 in the control section 8 (step 110).

Thus, when the setting processing of the DAC input data corresponding tothe upper limit fmax of the local oscillation frequency is finished, thesetting processing of the DAC input data corresponding to the lowerlimit fmin of the local oscillation frequency is performed in the sameway. That is, the PC 128 sends a command to the test signal generator126 to input the test signal at the same frequency as the lower limit ofthe variable range of the received frequency of the FM receiver 100 intothe FM receiver 100 (step 111). In addition, the PC 128 sends a commandto the control section 8 to set the local oscillation frequency so thatit may become a frequency corresponding to the lower limit fmin of thevariable range of the local oscillation frequency (step 112).

Thus, after various kinds of settings corresponding to the lower limitof the received frequency are finished, the PC 128 fetches the outputvalue of the level meter 122, and determines whether this value is thepredetermined value or higher (step 113). When the tracking errorbecomes large and the output value of the level meter 122 drops to thepredetermined value or lower, negative judgment is performed in thedetermination at step 113, and next, the PC 128 sets a value obtained bysubtracting or adding the predetermined value d₁ from or to the DACinput data D₀ corresponding to a median fc mentioned below (step 114) asthe DAC input data D₂ set when the local oscillation frequency is lowerthan a lower mean value f_(L) corresponding to the almost middle betweenthe median fc of the variable range, and the lower limit fmin, andwrites this setting value in the EEPROM 84 in the control section 8(step 115).

Furthermore, since such a value of d₁ that the tracking error may becomea predetermined value or less in the lower limit fmin of the variablerange of the local oscillation frequency is calculated beforehand byinputting the DAC input data D₂, obtained by addition or subtraction ofthis predetermined value d₁, instead of the DAC input data D₀ into theDAC 4 similarly to the addition or subtraction value d₀, it is made tobe able to suppress the tracking error in the range from the median fcto the lower limit fmin to the predetermined value or less only bychanging the value of the DAC input data into D₂ from D₀ at thefrequency in a predetermined range including this lower limit fmin whenthe tracking error in the lower limit fmin is large.

In addition, when the tracking error corresponding to the lower limitfmin of the local oscillation frequency is small and the output value ofthe level meter 122 is the predetermined value or higher, affirmativejudgment is performed in the determination at step 113, and next, the PC128 sets the value same as the DAC input data D₀ corresponding to themedian fc, mentioned above, as the DAC input data D₂ set when the localoscillation frequency is lower than the lower mean value f_(L)corresponding to the almost middle between the median fc of its variablerange and the lower limit fmin (step 116) to write this setting value inthe EEPROM 84 in the control section 8 (step 117).

FIGS. 6 and 7 are graphs showing the relationship between the variablerange of the local oscillation frequency and the tracking error in theFM receiver 100 of this embodiment.

As shown in FIG. 6, in the median fc of the local oscillation frequency,since the adjustment is performed so that the tracking error may becomeat a minimum, and the DAC input data D₀ which is inputted into the DACs4 and 6 is set, the tracking error in this frequency hardly exists. Inaddition, as the difference between this median fc and the actual localoscillation frequency becomes large, the tracking error also becomeslarge. Then, as shown in FIG. 6, when the tracking error in the upperlimit fmax or lower limit fmin of the local oscillation frequencyexceeds the predetermined value ε, the DAC input data D₁ and D₂ whosevalues are different from the DAC input data D₀ corresponding to thefrequency range including the median fc is set in the frequency range inor above the upper mean value f_(u) or the frequency range in or belowthe lower mean value f_(L), and hence, the tracking adjustment is madeso that the tracking error in these respective frequency ranges maybecome below or at the predetermined value ε as shown in FIG. 7.

Thus, since the tracking adjustment of the FM receiver 100 of thisembodiment is just to perform the measurement using the distortion meter120 and level meter 122 at the median fc of the local oscillationfrequency, it becomes possible to sharply shorten measuring time byreducing the number of times of the distortion rate measurement whichrequires comparatively long time for measurement.

Next, the operation in the case of receiving an FM broadcasting wave byusing the FM receiver 100 which is given the tracking adjustment in thisway will be simply explained. When a predetermined power switch (notshown) is operated and the FM receiver 100 is in an operable status, theMPU 81 in the control section 8 determines whether the operation section83 is operated and the modification of a received frequency iscommanded. When the modification of the received frequency is commanded,the MPU 81 calculates a division ratio of the frequency divider 32necessary for generating the local oscillation frequency correspondingto s received frequency after the change, and sets this calculateddivision ratio to the frequency divider 32. In addition, the MPU 81determines whether the local oscillation frequency corresponding to thereceived frequency after this change belongs to which frequency bandshown in FIG. 7, and inputs into each of the DACs 4 and 6 either of thecorresponding DAC input data D₀, D₁, and D₂. Owing to this, since thetracking error at the time when an FM broadcasting wave at a newreceived frequency is received is suppressed below or at a predeterminedvalue, it is possible to maintain a good receiving status in the entirearea of a receiving band.

In particular, in the FM receiver 100 of this embodiment, the VCOresonance circuit 91 included in the local oscillator 3 and twohigh-frequency tuning circuits 20 and 24 included in the high frequencyreceiving circuit 2 are achieved in similar structure, and further, whenthe control voltage Vc generated in the local oscillator 3 changes, thetuned voltages Vt1 and Vt2 applied to the respective high-frequencytuning circuits 20 and 24 also change with interlocking with this, andhence, the change of the tuning frequency is suppressed. For thisreason, a specific temperature compensation circuit becomes unnecessary.In addition, since operating with the control voltage Vc applied fromthe local oscillator 3 as a reference voltage, each of the DACs 4 and 6is not influenced even if a supply voltage of the FM receiver 100 isunstable, and hence, it is possible to prevent the increase of thetracking error by the fluctuation of the supply voltage.

In addition, the present invention is not limited to the above-mentionedembodiments, but various modified implementation is possible within thescope of the gist of the present invention. For example, in theembodiment mentioned above, when the tracking error measured on thebasis of the output value of the level meter 122 exceeds a predeterminedvalue in the upper limit fmax or lower limit fmin of the localoscillation frequency, the DAC input data D₁ and D₂ which is obtained sothat the tracking error may become below or at the predetermined valuebeforehand is used instead of the DAC input data D₀ set incorrespondence to the median fc of the local oscillation frequency, butit is also good to measure each time an adequate value of the DAC inputdata at which the tracking error becomes the predetermined value or lessby changing the value of the DAC input data with monitoring an amount ofthe tracking error by acquiring the output value of the level meter 122at these upper limit fmax or lower limit fmin.

Furthermore, although the value of the DAC input data is changed onlyonce from D₀ to D₁ or from D₀ to D₂ in the embodiment mentioned aboveaccording to necessity when the local oscillation frequency is higherthan the upper mean value f_(u), or is lower than the lower mean valuef_(L), it is also good to change the value of the DAC input data twiceor more in each.

Moreover, although the case that the tracking adjustment of the FMreceiver 100 is performed is explained in the embodiment mentionedabove, the present invention is applicable also to other receiversadopting a superheterodyne system, such as an AM receiver, a televisionset, and a cellular phone.

In addition, although the tuned voltages Vt1 and Vt2 which are appliedto two high-frequency tuning circuits 20 and 24 in the high frequencyreceiving circuit 2 respectively are separately generated in theembodiment mentioned above, it is also good to set each tuning frequencyby using a common tuned voltage Vt1 by adjusting device constants ofcomponents in the two high-frequency tuning circuits 20 and 24. In thiscase, since time and effort necessary for the tracking adjustment alsobecomes about half while the simplification of circuit configuration isattained since the DAC 6 and multiplier circuit 7 become unnecessary, itbecomes possible to sharply reduce the adjustment work hours performedin the production process of the FM receiver 100.

Furthermore, although the value of the DAC input data D₀ at which thetracking error becomes at a minimum is obtained by setting the localoscillation frequency at the median fc and performing measurement usingthe distortion meter 120 and level meter 122 when the trackingadjustment is performed in the embodiment mentioned above, the settingvalue of the local oscillation frequency is not limited to the medianfc, but it is also good to set it at an arbitrary value included in avariable frequency range except this. Specifically, depending on thecharacteristics of the variable capacitance diodes included in thehigh-frequency tuning circuits 20 and 24 or the VCO resonance circuit91, as shown in FIG. 6, when it is made that an amount of the trackingerror in the upper limit fmax of the local oscillation frequency and anamount of the tracking error in the lower limit fmin become equal, afrequency at which an amount of the tracking error becomes zero mayshift from the median fc of the local oscillation frequency. In such acase, by setting the local oscillation frequency at a value which isshifted by a predetermined amount from the median fc in the upper orlower side to perform the tracking adjustment, it is possible to obtainan adequate value of the DAC input data D₀ by which it is possible tofurther lessen the tracking error throughout the variable range of thelocal oscillation frequency.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the receiver of the present invention,since the tuned voltage is generated on the basis of the controlvoltage, it is not necessary to obtain a plurality of tuned voltages, atwhich a tracking error becomes at a minimum, by measurement like aconventional receiver using a digital-to-analog converter, and hence, itis possible to shorten the time necessary for tracking adjustment.

In addition, according to a tracking adjusting method of a receiver ofthe present invention, since the measurement of a tracking error isexecuted at an substantially center value of the variable range of areceived frequency, it is possible to shorten the time necessary for thetracking adjustment by reducing the number of times of this measurement.

1. A tracking adjusting method of performing tracking adjustment of areceiver which comprises: a high frequency receiving circuit receiving abroadcast wave at a received frequency according to a tuned voltage; alocal oscillator generating a local oscillation signal at a frequencyaccording to a control voltage; a mixing circuit mixing a signal, whichis outputted from the high frequency receiving circuit, and the localoscillation signal, and outputting an intermediate frequency signalcorresponding to a differential frequency thereof; an offset circuitsetting a predetermined offset voltage to the control voltage; and amultiplier circuit performing analog multiplication of a predeterminedmultiplier to the control voltage, and applies a voltage, which is thecontrol voltage passed through the offset circuit and the multipliercircuit, as the tuned voltage to the high frequency receiving circuit,the tracking adjusting method of a receiver characterized in comprising:a first step of setting a received frequency of the receiver at anarbitrary value included in its variable range and inputting apredetermined test signal having the same frequency as the receivedfrequency at this time into the high frequency receiving circuit; and asecond step of setting a value of the offset voltage set by the offsetcircuit so that a tracking error of the receiver after various kinds ofsettings being performed at the first step may become at a minimum. 2.The tracking adjusting method of a receiver according to claim 1,characterized in comprising a third step of changing and setting a valueof the offset voltage in regard to some frequency band in which theseupper limit or lower limit is included when a tracking error near theupper limit or lower limit of the variable range is large.
 3. A trackingadjusting method of performing tracking adjustment of a receiver whichcomprises: a high frequency receiving circuit receiving a broadcast waveat a received frequency according to a tuned voltage; a local oscillatorgenerating a local oscillation signal at a frequency according to acontrol voltage; a mixing circuit mixing a signal, which is outputtedfrom the high frequency receiving circuit, and the local oscillationsignal, and outputting an intermediate frequency signal corresponding toa differential frequency thereof; a digital-to-analog converter whichsets the offset voltage by adjusting input data while using the controlvoltage as a reference voltage; a multiplier circuit performing analogmultiplication of a predetermined multiplier to the control voltage;memory which stores the input data necessary for generation of theoffset voltage set so that a tracking error corresponding to the entirearea of a variable range of a frequency of the local oscillation signalmay become a predetermined value or less; and a voltage value settingunit which sets a value of the offset voltage corresponding to afrequency of the local oscillation signal by reading the input datastored in the memory, and inputting it into the digital-to-analogconverter, and applies a voltage, which is the control voltage passedthrough the digital-to-analog converter and the multiplier circuit, asthe tuned voltage to the high frequency receiving circuit, the trackingadjusting method of a receiver characterized in comprising: a fourthstep of setting a received frequency of the receiver at an arbitraryvalue included in its variable range and inputting a predetermined testsignal having the same frequency as the received frequency at this timeinto the receiver; a fifth step of setting input data of thedigital-to-analog converter so that a tracking error of the receiverafter various kinds of settings being performed at the fourth step maybecome at a minimum; and a sixth step of storing the input data, set atthe fifth step, in the memory.
 4. The tracking adjusting method of areceiver according to claim 3, characterized in comprising: a seventhstep of changing and setting contents of input data of thedigital-to-analog converter in regard to some frequency band in whichthese upper limit or lower limit is included when a tracking error nearthe upper limit or lower limit of the variable range is large; and aneighth step of storing input data of the digital-to-analog converterafter change, set at the seventh step, in the memory.